开罗五角反铁磁体Bi2Fe4O9的二聚体物理
Dimer Physics in the Frustrated Cairo Pentagonal Antiferromagnet Bi2Fe4O9
摘要：
三角形网格是磁阻挫研究的主要领域，但在五边形网格中也可以观察到奇异的现象。一个特殊的非共线磁秩序确实是已知的稳定在Bi2Fe4O9实现开罗五边形晶格。我们提出的自旋波激发的磁有序状态，获得非弹性中子散射。它们揭示了一种与自旋对的局域旋进有关的非常规激发态。然后对磁激发进行建模，以确定超交换相互作用，对于该超交换相互作用，挫折确实是在自旋排列的起源处。这种分析揭示了相互作用中的层次结构，导致顺磁状态（接近内尔温度），由强耦合的二聚体组成，这些二聚体被更少的相关自旋分开。这产生了两种类型的响应与两个不等价的Fe站点，如在使用极化中子获得的磁化强度分布中观察到的所施加的磁场。
英文摘要：
The research field of magnetic frustration is dominated by triangle-based lattices but exotic phenomena can also be observed in pentagonal networks. A peculiar noncollinear magnetic order is indeed known to be stabilized in Bi2Fe4O9 materializing a Cairo pentagonal lattice. We present the spin wave excitations in the magnetically ordered state, obtained by inelastic neutron scattering. They reveal an unconventional excited state related to local precession of pairs of spins. The magnetic excitations are then modeled to determine the superexchange interactions for which the frustration is indeed at the origin of the spin arrangement. This analysis unveils a hierarchy in the interactions, leading to a paramagnetic state (close to the Néel temperature) constituted of strongly coupled dimers separated by much less correlated spins. This produces two types of response to an applied magnetic field associated with the two nonequivalent Fe sites, as observed in the magnetization distributions obtained using polarized neutrons.
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